1. Scope of the Invention
This invention relates to a continuous-time delta sigma analog digital converter for converting an analog input signal to a digital output signal, comprising:                an analog filter which filters the analog input signal and has at least one integration capacitor,        a quantifier operated in cycled fashion, which quantifier quantifies the filtered analog signal transmitted by the analog filter for generating the digital output signal, and        a feedback device with at least one digital analog converter, which device transmits at least one analog feedback signal to the analog filter on the basis of the digital output signal.        
Further, this invention relates to a method for continuous-time delta-sigma analog digital conversion for converting an analog input signal to a digital output signal, comprising:                analog filtering of the input signal using at least one integration capacitor,        a cycled quantification of the filtered analog signal for generating the digital output signal, and        a feedback comprising at least one digital analog conversion for supplying at least one analog feedback signal on the basis of the digital output signal for the analog filtering.        
2. Description of the State of the Art
Such a converter and such a conversion method are disclosed, for example, in DE 103 42 057 A1 and WO 97/26708. In this state of the art the digital output signal of the quantifier is simultaneously transmitted to two digital analog converters and the converted (analog) signals are fed back to the analog filter at respective summation nodes.
A fundamental problem with conventional continuous-time delta-sigma analog digital converters is the interval of time, which is unavoidable in practice, between the time of quantification and the time of output and feedback of the digital output signal. The stability of the converter is adversely affected by this delay. Furthermore, the feedback devices (digital analog converter, summating amplifier, etc.) are relatively expensive and/or consume a great deal of power in the case of delta-sigma analog digital converters of prior art.